Degradation kinetics of target compounds and correlations with spectral indices during UV/H2O2 post-treatment of biologically treated acrylonitrile wastewater

Abstract

In this study, the post-treatment of biologically treated acrylonitrile wastewater was investigated during UV/H₂O₂ process. Five contaminants in the effluent were selected as target compounds, including Furmaronitrile (FMN), 3-Pyridinecarbonitrile (3PCN), 1,3-Dicyanobenzene (1,3-DCB), 5-Methyl-1H-benzotriazole (5MBT), and 7-Azaindole (7AID). Under optimal reaction conditions, the UV/H₂O₂ post-treatment exhibited good performances in destruction of organic compounds and toxicity. The photo-chemical parameters of the target compounds were measured and it was found that 5MBT and 3PCN had fast degradation rate constants under direct UV photolysis. The second-order rate constants of the target compounds with hydroxyl radicals were determined to be in the range of (1.0-5.0) × 10⁹ M^-1 s^-1 at pH 3.0 and 25 °C. A simplified pseudo-first-order steady state (Sim-PSS) model, which considered direct UV photolysis and radical oxidation simultaneously, agreed well with the experimental data from the post-treatment of a biologically treated effluent. High-performance size exclusion chromatography (HPSEC) coupled with diode-array detector (DAD) and fluorescence detector (FLD) analysis revealed that humic-like sub-peak signals from different molecular weights of fluorescent organic matter decreased consistently during the oxidation process, which made humic-like fluorescence exhibit higher correlation with the target compounds' degradation than the spectral indices of UV absorbance at 254 nm (UVA₂₅₄) and protein-like fluorescence.

Keywords: Biologically treated acrylonitrile wastewater; Simplified pseudo-first-order steady state model; Spectral indices; Target compounds; UV/H(2)O(2) post-treatment.